Liquid ejection head and liquid ejection apparatus

ABSTRACT

A liquid ejection head includes a substrate in which a pressure generating chamber that communicates with a nozzle opening is formed; and a piezoelectric element having a piezoelectric layer, a first electrode that is formed on a surface of the piezoelectric layer on a side of the substrate so as to correspond to the pressure generating chamber, and a second electrode that is formed on a surface of the piezoelectric layer opposite to the side on which the first electrode is formed so as to extend over a plurality of the pressure generating chambers, wherein the second electrode is formed to extend to an outside of the pressure generating chamber in a longitudinal direction of the pressure generating chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation patent application of U.S. application Ser. No.14/565,942, filed Dec. 10, 2014, which is a divisional patentapplication of U.S. application Ser. No. 14/244,250, filed Apr. 3, 2014,which is a continuation patent application of U.S. application Ser. No.13/755,342, filed Jan. 31, 2013, now U.S. Pat. No. 8,727,510, issued May20, 2014, which claims priority to Japanese Patent Application No.2012-019569, filed Feb. 1, 2012, all of which are incorporated byreference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to liquid ejection heads and liquidejection apparatuses.

2. Related Art

JP-A-2009-172878 and JP-A-2009-196329 disclose a liquid ejection headincluding a substrate in which a pressure generating chamber thatcommunicates with a nozzle opening for ejecting liquid is formed, and apiezoelectric element having a piezoelectric layer, a lower electrodethat is formed on the lower side of the piezoelectric layer and an upperelectrode that is formed on the upper side of the piezoelectric layer.In such a liquid ejection head, the lower electrode is provided as anindividual electrode that corresponds to each of the pressure generatingchambers, and the upper electrode is provided as a common electrode fora plurality of piezoelectric elements that correspond to a plurality ofpressure generating chambers.

The above-mentioned piezoelectric element displaces when a voltage isapplied across both electrodes and flexes into the pressure generatingchamber. During flexing, a significant amount of stress is generated atthe interface between an area on the piezoelectric element where theupper electrode, the piezoelectric layer and the lower electrode overlap(active section) and an area other than the active section (inactivesection), which causes distortion to be concentrated at this position.Since concentration of distortion may cause a problem such as crack inthe piezoelectric layer that forms the piezoelectric element, it hasbeen required to prevent such a problem. Further, in addition toprevention of the above-mentioned problem, it has been also required toincrease the amount of liquid to be output (ejected) from the pressuregenerating chamber to the outside of the nozzle opening by usingdeformation of the vibration plate in response to flexing of thepiezoelectric element, thereby improving performance of the liquidejection head.

SUMMARY

An advantage of some aspects of the invention is that a liquid ejectionhead capable of preventing or reducing a problem such as cracking in apiezoelectric layer and increasing the amount of liquid to be ejected,and a liquid ejection apparatus having the same are provided.

According to an aspect of the invention, a liquid ejection headincludes: a substrate in which a pressure generating chamber thatcommunicates with a nozzle opening is formed; and a piezoelectricelement having a piezoelectric layer, a first electrode that is formedon a surface of the piezoelectric layer on a side of the substrate so asto correspond to the pressure generating chamber, and a second electrodethat is formed on a surface of the piezoelectric layer opposite to theside on which the first electrode is formed so as to extend over aplurality of the pressure generating chambers, wherein the secondelectrode is formed to extend to an outside of the pressure generatingchamber in a longitudinal direction of the pressure generating chamber.With this configuration, the second electrode is formed to extend to theoutside of the pressure generating chamber in the longitudinal directionof the pressure generating chamber. Accordingly, concentration ofdistortion at the interface on the piezoelectric element is reducedcompared to the case in which the second electrode is formed not toextend to the outside of the pressure generating chamber in thelongitudinal direction, thereby reducing a problem such as cracking.Further, since the resistance to cracking of the piezoelectric elementis improved, voltage resistance to the piezoelectric element is alsoimproved.

According to an aspect of the invention, an area where the firstelectrode, the piezoelectric layer and the second electrode overlap maybe formed to extend to an outside of the pressure generating chamber inthe longitudinal direction. That is, since the area where the firstelectrode, the piezoelectric layer and the second electrode overlap(active section) is an area which drives when a voltage is applied,concentration of distortion at the interface on the piezoelectricelement is reduced by providing the active section to extend to theoutside of the pressure generating chamber in the longitudinaldirection, thereby reducing a problem such as cracking.

According to an aspect of the invention, an opening is formed on thepiezoelectric layer by removing the piezoelectric layer at a positionthat substantially corresponds to an area between the pressuregenerating chambers, and the opening may be formed to extend to anoutside of the pressure generating chamber in the longitudinaldirection. With this configuration, since the opening is formed toextend to the outside of the pressure generating chamber in thelongitudinal direction, a displacement amount of the piezoelectricelement at the end portions of the pressure generating chamberincreases, which results in increased amount of liquid ejected byflexing of the piezoelectric element.

According to an aspect of the invention, a metal layer that is disposedon the second electrode and serves as a wiring may be formed to extendto both inside and outside of the pressure generating chamber. With thisconfiguration, since the metal layer is formed to extend to both insideand outside of the pressure generating chamber, concentration ofdistortion at the interface on the piezoelectric element is furtherreduced, thereby reducing a problem such as cracking.

The technical concept of the invention is not limited to the form ofliquid ejection head, and for example, a liquid ejection apparatushaving the liquid ejection head in any of the aspects described abovemay be regarded as one aspect of the invention. Further, a manufacturingmethod including a manufacturing step of piezoelectric element, liquidejection head and liquid ejection apparatus in any of the aspectsdescribed above (for example, a manufacturing method of piezoelectricelement, manufacturing method of liquid ejection head and manufacturingmethod of liquid ejection apparatus) may be regarded as one aspect ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the accompanying drawings, wherein like numbers referencelike elements.

FIG. 1 is an exploded perspective view which schematically shows arecording head.

FIG. 2 is a sectional view of the recording head in a plane parallel tothe longitudinal direction.

FIG. 3 is a plan view of an area on a substrate.

FIGS. 4A, 4B and 4C are sectional views taken along the respective linesof FIG. 3.

FIGS. 5A, 5B and 5C are views which show part of manufacturing steps ofa piezoelectric element in sequence.

FIGS. 6A, 6B and 6C are views which show part of manufacturing steps ofa piezoelectric element in sequence.

FIG. 7 is a plan view of an area on a substrate according to a modifiedexample.

FIG. 8 is a view which explains an effect of the modified example.

FIG. 9 is a schematic view of an example of an ink jet recordingapparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS 1. General Configuration of LiquidEjection Head

An embodiment of the invention will be described below with reference tothe drawings. FIG. 1 is an exploded perspective view which schematicallyshows an ink jet recording head 1 (hereinafter, referred to as recordinghead 1) which is an example of liquid ejection head. FIG. 2 is avertical sectional view of the recording head 1 in a plane parallel tothe longitudinal direction of a pressure generating chambers 12 andpassing through a lower electrode film 2 that corresponds to one of thepressure generating chambers 12. The recording head 1 includes asubstrate (flow path forming substrate) 10. The substrate 10 is formedof, for example, a silicon single crystal substrate with a vibrationplate 50 disposed on one side thereof. The vibration plate 50 includes,for example, an elastic film 51 formed of an oxide film that is incontact with the substrate 10, and an insulator film 55 formed of anoxide film made of a material different from that of the elastic film 51and stacked on the elastic film 51. A plurality of pressure generatingchambers 12 that are separated by dividing walls 11 are arranged side byside in the short direction (width direction) thereof on the substrate10, and one side of the pressure generating chambers 12 are closed bythe vibration plate 50.

In the substrate 10, ink supply paths 14 that are separated by thedividing walls 11 and communicate with the respective pressuregenerating chambers 12 are formed at one end of the pressure generatingchambers 12 in the longitudinal direction. Further, a communicationsection 13 that communicates with the respective ink supply paths 14 isformed on the outer side of the ink supply paths 14. The communicationsection 13 communicates with a reservoir section 31 of a protectivesubstrate 30, which will be described later, so as to form part of areservoir 9 that serves as an ink chamber (liquid chamber) for all thepressure generating chambers 12.

Each ink supply path 14 has a cross sectional area in the widthdirection smaller than that of the pressure generating chamber 12 so asto keep a flow path resistance of ink that is introduced from thecommunication section 13 into the pressure generating chambers 12 to beconstant. Although the ink supply path 14 is narrower in the widthdirection thereof, instead or as well it may be thinner in the thicknessdirection of the substrate 10 so as to have a cross sectional areasmaller than that of the pressure generating chamber 12. The material ofthe substrate 10 is not limited to a silicon single crystal substrate,and may include a glass ceramic material, stainless steel, etc.

A nozzles plate 20 is secured by using an adhesive, a heat adhesive filmor the like on the surface of the substrate 10 opposite to the side onwhich the vibration plate 50 is disposed. Nozzle openings 21 thatcorrespond to the respective pressure generating chambers 12 are formedon the nozzles plate 20 by drilling at positions adjacent to the otherend of the pressure generating chambers 12 in the longitudinaldirection. The nozzles plate 20 is formed of, for example, a glassceramic material, silicon single crystal substrate, stainless steel,etc.

A plurality of piezoelectric elements 3 having the lower electrode film2, a piezoelectric layer 5 and an upper electrode film 4 are formed onthe surface of the vibration plate 50 opposite to the side of thesubstrate 10 and arranged side by side in the width direction thereof.The piezoelectric elements 3 are formed so as to correspond to therespective pressure generating chambers 12. The lower electrode film 2is defined as a first electrode which is formed on the surface of thepiezoelectric layer 5 on the side of the substrate 10 and corresponds toeach of the pressure generating chambers 12. On the other hand, theupper electrode film 4 is defined as a second electrode which is formedon the surface of the piezoelectric layer 5 opposite to the side onwhich the first electrode of the piezoelectric layer 5 is formed andextends across an area that corresponds to the plurality of pressuregenerating chambers 12. The piezoelectric element 3 includes an area(active section) where the lower electrode film 2, the piezoelectriclayer 5 and the upper electrode film 4 overlap. Further, thepiezoelectric element 3 and the vibration plate 50 that is displaced bydriving the piezoelectric element 3 are collectively defined as anactuator device. Generally, in the piezoelectric element 3, one of theelectrodes disposed on each side of the piezoelectric layer 5 isconfigured as a common electrode, and the other is configured as anindividual electrode. In this embodiment, the lower electrode film 2serves as the individual electrode for each of the piezoelectricelements 3 that correspond to the respective pressure generatingchambers 12, and the upper electrode film 4 serves as the commonelectrode for all the pressure generating chambers 12 that correspond tothe piezoelectric element 3.

As shown in FIG. 1, a plurality of recesses are formed as openings 5 ain the piezoelectric layer 5 by removing the piezoelectric layer 5. Theplurality of openings 5 a are arranged side by side in the widthdirection thereof and are formed at positions that substantiallycorrespond to between each of the pressure generating chambers 12. Inother words, each of the piezoelectric elements 3 including the activesection are formed between the openings 5 a so as to correspond to eachof the pressure generating chambers 12. The surface of the openings 5 aare covered by the upper electrode film 4.

The protective substrate 30 with a compliance substrate 40 being securedthereon is mounted on the surface of the vibration plate 50 on which thepiezoelectric elements are formed. In this embodiment, description willbe appropriately made taking the side of the compliance substrate 40 inthe recording head 1 as the upper side, and the side of the nozzlesplate 20 as the lower side for reference purposes of only. Theprotective substrate 30 including a piezoelectric element holdingsection 32 is attached by using an adhesive 35 on the surface of thevibration plate 50 on which the piezoelectric elements 3 are formed. Thepiezoelectric element holding section 32 is positioned so as to opposethe piezoelectric elements 3 and has an inner space that is sized so asnot to interfere with the movement of the piezoelectric elements 3.Since the piezoelectric elements 3 are disposed inside the piezoelectricelement holding section 32, they are substantially protected from theoutside environment. Further, the protective substrate 30 also includesthe reservoir section 31 formed at a position that corresponds to thecommunication section 13 of the substrate 10. The reservoir section 31,for example, penetrates through the protective substrate 30 in thethickness direction and extends in the width direction of the pressuregenerating chambers 12, and accordingly, communicates with thecommunication section 13 of the substrate 10 as described above, therebyforming a reservoir 9. Although the material of the protective substrate30 may include a glass, ceramics material, metal, resin etc., it ispreferable to be a material having substantially the same thermalexpansion rate as that of the substrate 10. In this embodiment, theprotective substrate 30 is formed of a silicon single crystallinesubstrate, which is the same material as that of the substrate 10.

As shown in FIG. 2, a lead electrode 60 is connected to the upperelectrode film 4 which is the common electrode, while a lead electrode61 is connected to the lower electrode film 2 which is the individualelectrode. The lead electrodes 60, 61 and a through hole 5 b (which willbe described later) that extends through the piezoelectric layer 5 forconnecting the lead electrode 61 to the lower electrode film 2 are notshown in FIG. 1. The lead electrodes 60, 61 are connected to a drivecircuit 120 (FIG. 1) on which a drive IC for driving the piezoelectricelements 3 and the like are mounted via leads, which are not shown inthe figure. The lead electrode 60 is a metal layer disposed on thesecond electrode and serves as wirings. Although in the example shown inFIG. 2, the lead electrode 61 that is connected to the individualelectrode is disposed on the other end in the longitudinal direction,the lead electrode 61 may be disposed on one side in the longitudinaldirection.

Further, the compliance substrate 40 composed of a sealing film 41 and afixation plate 42 is attached on the protective substrate 30. Thesealing film 41 is made of a flexible material having a low rigidity,and one side of the reservoir section 31 is sealed by the sealing film41. The fixation plate 42 is made of a rigid material such as a metal.Since an area of the fixation plate 42 which opposes the reservoir 9 iscompletely removed in the thickness direction to form an opening 43, oneside of the reservoir 9 is sealed only by the flexible sealing film 41.

In the recording head 1, ink is introduced from an external ink supplyunit, which is not shown in the figure. After ink fills the inside ofthe path from the reservoir 9 to the nozzle opening 21, a voltage isapplied to each of the piezoelectric elements 3 that correspond to thepressure generating chambers 12 in response to recording signals fromthe drive IC so that the piezoelectric elements 3 are flexibly deformed.As a result, a pressure in the pressure generating chambers 12increases, thereby allowing ink droplets (liquid) to be output (ejected)from the nozzle openings 21.

2. Range of the Active Section

Next, a configuration of the piezoelectric element 3 is described indetail with further reference to FIGS. 1, 2 and also FIGS. 3, 4. FIG. 3is a plan view of an area of the substrate 10 in which the piezoelectricelement 3 that corresponds to one pressure generating chamber 12 isformed. FIG. 4A is a vertical sectional view taken along the lineIVA-IVA of FIG. 3, FIG. 4B is a vertical sectional view taken along theline IVB-IVB of FIG. 3, and FIG. 4C is a vertical sectional view takenalong the line IVC-IVC of FIG. 3.

The outline of the pressure generating chamber 12 and the ink supplypath 14 that communicates with the pressure generating chamber 12 isillustrated in FIG. 3 by the dashed two dotted line. Although theoutline of the pressure generating chamber 12 and the ink supply path 14shown in FIG. 3 is slightly different from that of FIGS. 1 and 2, eithermay be employed. In FIG. 3, a range of the lower electrode film 2 as theindividual electrode is indicated by the thin dotted line, a range ofthe piezoelectric layer 5 is indicated by the bold dotted line, and arange of the upper electrode film 4 as the common electrode is indicatedby the gray-colored area. Further, in FIG. 3, a range of the leadelectrode 60 that is partially stacked on the upper electrode film 4 anda range of lead electrode 61 that is partially stacked on thepiezoelectric layer 5 are illustrated by hatching. The through hole 5 bis formed on the piezoelectric layer 5 such that the lead electrode 61is electrically connected to the lower electrode film 2 via the throughhole 5 b.

The lower electrode film 2 has a length in the width direction which issmaller than that of the pressure generating chambers 12 and a length inthe longitudinal direction larger than the pressure generating chambers12. Specifically, one end of the lower electrode film 2 in thelongitudinal direction extends to the position of the ink supply paths14, while the other end extends over the end of the pressure generatingchambers 12. Further, the lower electrode film 2 is covered by thepiezoelectric layer 5 except for a range that faces the through hole 5b. Accordingly, a leak current from the lower electrode film 2 can bereduced to a minimum, thereby eliminating a particular measure to reducethe leak current (for example, protection by using a protective filmmade of a material such as aluminum oxide).

The openings 5 a are formed at positions that substantially correspondto part of the dividing walls 11 which are located on both sides of thepressure generating chambers 12 in the width direction. As shown in FIG.4B, the openings 5 a are formed by removing the piezoelectric layer 5.Since such openings 5 a are formed, the piezoelectric layer 5 on thepressure generating chambers 12 is mostly included within the pressuregenerating chambers 12 in the width direction, while both ends of thepiezoelectric layer 5 extend to the outside of the pressure generatingchambers 12 in the longitudinal direction so as to completely cover thelength of the pressure generating chambers 12. The upper electrode film4 extend to the outside of the pressure generating chambers 12 both inthe width direction and the longitudinal direction so as to completelycover the length of the pressure generating chambers 12. That is, inthis embodiment, the active sections that correspond to the respectivepressure generating chambers 12 extend to the outside of the pressuregenerating chambers 12 in the longitudinal direction. As shown in FIG.3, the length of the active section in the longitudinal direction isdefined as L1, and the length of the pressure generating chambers 12 inthe longitudinal direction is defined as L2 such that L1 covers therange of L2.

The configurations of FIG. 3 are repeatedly disposed in the widthdirection on the substrate 10 (more specifically, on the insulator film55) so as to correspond to the pressure generating chambers 12.Accordingly, the piezoelectric layer 5, the upper electrode film 4 andthe lead electrode 60 are repeatedly disposed in the width direction(see FIG. 1 as appropriate). Further, two lead electrodes 60 of FIG. 3(the lead electrode 60 as shown in FIG. 4A and the lead electrode 60 asshown in FIG. 4C) are connected to each other at a specified position,which is not shown in the figure, so as to form one common electrode.

In this embodiment, both ends of the active section in the longitudinaldirection of the pressure generating chamber 12 are configured to extendto the outside of the pressure generating chamber 12. Accordingly, whenthe active section of the piezoelectric element 3 drives to flexiblydeform the piezoelectric element 3, concentration of distortion at theinterface between the active section and the inactive section of thepiezoelectric element 3 is reduced compared to the case in which bothends of the active section in the longitudinal direction of the pressuregenerating chamber 12 are configured not to extend to the outside of thepressure generating chamber 12, thereby reducing a problem such ascracking of the piezoelectric layer 5. Further, since the resistance tocracking of the piezoelectric element 3 is improved, voltage resistanceto the piezoelectric element 3 is also improved.

As seen from FIGS. 2 and 3, the lead electrode 60 of this embodimentextends on both the inside and outside of the pressure generatingchamber 12 (across the end of the pressure generating chambers 12). Withthis arrangement of the lead electrode 60, concentration of distortionat the interface between the active section and the inactive section ofthe piezoelectric element 3 or at the proximity of both ends of thepiezoelectric element 3 is reduced, thereby further effectively reducinga problem such as cracking.

The opening 5 a serves to provide the active section with a springproperty by reducing the thickness of the circumference of the activesection. Accordingly, the size of the opening 5 a significantly effectson the flexibility of the active section. In this embodiment, as seenfrom FIG. 3, a length L3 of the opening 5 a in the longitudinaldirection is within the length L2 of the pressure generating chambers12. That is, both ends of the opening 5 a in the longitudinal directionare located at the inner side of both ends of the pressure generatingchambers 12. Accordingly, the piezoelectric layer 5 overlaps both endsof the pressure generating chambers 12 in the longitudinal direction,thereby increasing rigidity of the piezoelectric element 3 at theproximity of both ends of the pressure generating chambers 12. As aresult, concentration of distortion at the interface between the activesection and the inactive section of the piezoelectric element 3 or atthe proximity of both ends of the piezoelectric element 3 is reduced,thereby further effectively reducing a problem such as cracking.

3. Manufacturing Method

Next, an example of manufacturing method of the recording head 1according to this embodiment will be described below. FIGS. 5A, 5B, 5Cand FIGS. 6A, 6B, 6C show manufacturing steps of the piezoelectricelement 3 that constitutes the recording head 1 in sequence. FIGS. 5A,5B, 5C and FIGS. 6A, 6B, 6C are combination of vertical sectional viewsas seen from the same view point as that of FIG. 2 in a plane parallelto the longitudinal direction and vertical sectional views taken alongthe line D-D′ in the respective figures, showing progress in themanufacturing steps. In FIGS. 5A, 5B, 5C and FIGS. 6A, 6B, 6C,components other than those of the piezoelectric element 3, for example,the substrate 10 are not shown as appropriate. First, the elastic film51 formed of silicon dioxide (SiO₂) and the insulator film 55 formed ofzirconium oxide (ZrO₂) are formed on the silicon single crystalsubstrate (not shown in the figure) which is a material of the substrate10 (for example, see JP-A-2005-8841). Then, a lower electrode film isformed by laminating platinum and iridium on the insulator film 55, forexample, by a sputtering technique. After that, a thin piezoelectriclayer is formed on the lower electrode film, for example, by a sol-gelprocess. The thin piezoelectric layer as used herein means that thepiezoelectric layer has a thickness at least smaller than that of thepiezoelectric layer 5 which is required in the resultant piezoelectricelement 3.

Then, photo-etching is performed on the lower electrode film and thepiezoelectric layer to make patterning on the lower electrode film andthe piezoelectric layer so as to form a specific pattern thatcorresponds to the respective positions where the pressure generatingchambers 12 are to be formed. FIG. 5A shows the lower electrode film 2and the piezoelectric layer 500 on the lower electrode film 2 that havebeen formed by the above-mentioned patterning. In the state shown inFIG. 5A, the piezoelectric layer is further formed to a thicknessrequired in the resultant piezoelectric element 3, for example, by asol-gel process, and then, a thin upper electrode film formed of iridiumor the like is formed on the piezoelectric layer, for example, by asputtering technique. The thin upper electrode film as used herein meansthat the upper electrode film has a thickness at least smaller than thatof the upper electrode film 4 which is required in the resultantpiezoelectric element 3. FIG. 5B shows the piezoelectric layer 501 andthe upper electrode film 400 on the piezoelectric layer 501 that havebeen formed in the steps so far.

Then, in the state shown in FIG. 5B, photo-etching is performed on theupper electrode film 400 and the piezoelectric layer 501 to makepatterning that leaves a specific thickness of the piezoelectric layerthat covers the lower electrode film 2 and the upper electrode film onthe piezoelectric layer. That is, a recess that corresponds to theopening 5 a is formed. In this embodiment, etching of the piezoelectriclayer for forming the opening 5 a is referred to as “first etchingprocess of the piezoelectric layer” as appropriate. FIG. 5C shows thepiezoelectric layer 502 and the upper electrode film 401 on thepiezoelectric layer 502 that have been formed in the steps so far.

Then, in the state shown in FIG. 5C, photo-etching is performed on theupper electrode film 401 and the piezoelectric layer 502 to form thethrough hole 5 b that allows part of the lower electrode film 2 to beexposed. In this embodiment, etching of the piezoelectric layer forforming the through holes 5 b is referred to as “second etching processof the piezoelectric layer” as appropriate. FIG. 6A shows thepiezoelectric layer 5 and the upper electrode film 402 on thepiezoelectric layer 5 that have been formed in the steps so far. Asshown in FIG. 6A, the through hole 5 b penetrates through thepiezoelectric layer 5 and the upper electrode film 402. According tothis embodiment, in the state subsequent to that shown in FIG. 5B,etching of the piezoelectric layer for forming the opening 5 a andetching of the piezoelectric layer for forming the through hole 5 b areseparately performed, whose reason will be described later.

Then, in the state shown in FIG. 6A, the upper electrode film is furtherformed to a thickness required in the resultant piezoelectric element 3,for example, by a sputtering technique. After that, photo-etching isperformed on the upper electrode film to make patterning on the upperelectrode film so as to form a specific pattern that corresponds to therespective positions where the pressure generating chambers 12 are to beformed and a specific pattern that includes the range of the respectivethrough holes (see FIG. 3). FIG. 6B shows the upper electrode film 4that has been formed by the above-mentioned patterning. Then, in thestate shown in FIG. 6B, a metal layer (for example, the metal layerincluding gold (Au) and Nichrome (NiCr)) which is a material of the leadelectrodes 60, 61 is formed, for example, by a sputtering technique, andthen, photo-etching is performed on the metal layer so as to form thelead electrodes 60, 61. The lead electrode 60 is connected to the upperelectrode film 4. On the other hand, the lead electrode 61 is connectedto the lower electrode film 2 via the through hole 5 b and the upperelectrode film 4 (FIG. 6B) formed on the surface of the through hole 5b. The upper electrode film 4 (FIG. 6B) formed on the surface of thethrough hole 5 b serves as part of the wirings that connect the drivecircuit 120 and the individual electrode (the lower electrode film 2).

FIG. 6C shows a configuration that has been formed in the steps so far.The configuration shown in FIG. 6C is consistent with the configurationof the piezoelectric element 3 shown in FIG. 2 and FIG. 3. Then, therecording head 1 is completed through the steps such as connecting ofthe protective substrate 30 on the side of the piezoelectric element 3,forming of the pressure generating chambers 12, the ink supply paths 14and the like by etching the substrate 10, connecting of the nozzlesplate 20 on the substrate 10, and connecting of the compliance substrate40 on the protective substrate 30. It should be noted that theabove-mentioned manufacturing method of the recording head 1 is merelyan example, and various modifications are possible. The forming methodof the piezoelectric layer is also not limited to that described above,and a sputtering technique may also be used. Further, the material ofthe piezoelectric layer may include various materials, for example, leadzirconate titanate based material and non-lead (lead-free) perovskiteoxide such as barium titanate.

Then, the reason of the first etching process of the piezoelectric layerand the second etching process of the piezoelectric layer beingseparately provided in the above-mentioned manufacturing method will bedescribed. When the piezoelectric layer 501 is formed so as to cover thelower electrode film 2 and the insulator film 55 around the lowerelectrode film 2 as shown in FIG. 5B, it is not always possible due tomanufacturing accuracy to easily make the thickness of the piezoelectriclayer 501 on the insulator film 55 and the thickness of thepiezoelectric layer 501 on the lower electrode film 2 to be the same.Particularly, uneven thickness of those layers becomes significant whenthe piezoelectric layer is formed by using liquid, typically by asol-gel process. Accordingly, the optimum etching amount of thepiezoelectric layer 501 to expose the insulator film 55 (to form theopening 5 a) is different from the optimum etching amount of thepiezoelectric layer 501 to expose the lower electrode film 2 (to formthe through hole 5 b). If etching for exposing the insulator film 55 andetching for exposing the lower electrode film 2 are simultaneouslyperformed, one of the insulator film 55 and the lower electrode film 2may suffer from over etching (excessive etching) and the other maysuffer from under etching (insufficient etching), since it is difficultto precisely control the etching amount at each location.

For example, when the thickness of the piezoelectric layer 501 on theinsulator film 55 is greater than the thickness of the piezoelectriclayer 501 on the lower electrode film 2 and etching of those layers aresimultaneously performed, the lower electrode film 2 suffers from overetching during removing of the piezoelectric layer 501 on the insulatorfilm 55, which may cause breakage of the lower electrode film 2.Further, in an attempt to prevent over etching of the lower electrodefilm 2, the insulator film 55 may fail to be exposed. Alternatively,when the thickness of the piezoelectric layer 501 on the insulator film55 is smaller than the thickness of the piezoelectric layer 501 on thelower electrode film 2 and etching of those layers are simultaneouslyperformed, the insulator film 55 suffers from over etching duringremoving of the piezoelectric layer 501 on the lower electrode film 2.As a result, the opening 5 a is thinner than the required thickness andfails to obtain the required rigidity, which may cause cracking on theopening 5 a. Further, in an attempt to prevent over etching of theinsulator film 55, the lower electrode film 2 may fail to be exposed.

Therefore, in this embodiment, the first etching process of thepiezoelectric layer and the second etching process of the piezoelectriclayer are separately provided so that optimum etching amount of thepiezoelectric layer is set to obtain the thickness for each area to beprocessed in each process. Accordingly, optimum etching of thepiezoelectric layer 501 to form the opening 5 a and optimum etching ofthe piezoelectric layer 501 to form the through hole 5 b can beachieved, thereby preventing the above-mentioned over etching and underetching from occurred. The first etching process of the piezoelectriclayer and the second etching process of the piezoelectric layer may beperformed in the order opposite to that is described in the abovedescription.

4. Modified Example

The invention is not limited to the above-mentioned embodiment and canbe implemented in various embodiments within the scope of the inventionwithout departing from its principle. For example, the followingmodified example can be implemented. Further, the various embodimentsand modified examples which are combined as appropriate are also withinthe scope of the invention. In the following description, differencesfrom the above-mentioned embodiment will be described, andconfigurations and effects which are the same as those of theabove-mentioned embodiment will be omitted as appropriate.

FIG. 7 is a plan view of an area on the substrate 10 according to amodified example, and similarly to FIG. 3, shows the area in which thepiezoelectric element 3 that corresponds to one pressure generatingchamber 12 is formed. The configuration of FIG. 7 and the configurationof FIG. 3 are different in that they have different lengths of theopening 5 a in the longitudinal direction. Specifically, the opening 5 aof FIG. 7 is longer than that of FIG. 3, and the opening 5 a of FIG. 7is formed to extend to the outside of the pressure generating chamber 12in the longitudinal direction. That is, in FIG. 7, the length L3 of theopening 5 a in the longitudinal direction is formed to include thelength L2 of the pressure generating chamber 12. With thisconfiguration, a rigidity of the piezoelectric element 3 at theproximity of both ends of the pressure generating chambers 12 in thelongitudinal direction decreases, and a displacement amount of thepiezoelectric element 3 at the proximity of both the pressure generatingchamber 12 increases.

FIG. 8 is a view which explains an effect of the modified example. FIG.8 illustrates the positional relationship between the pressuregenerating chamber 12 in the longitudinal direction and the elastic film51 that closes the upper portion of the pressure generating chamber 12in a simplified manner. When a voltage is applied to the piezoelectricelement 3 that is formed to correspond to the pressure generatingchamber 12 to drive the active section, the active section displaces andthe elastic film 51 flexes into the pressure generating chamber 12. Thedifference between the position before the elastic film 51 flexes (theposition of the elastic film 51 indicated by the solid line in FIG. 8)and the position after the elastic film 51 flexes in the up-downdirection is the displacement amount Ah. Further, in FIG. 8, thepositions of the flexed elastic film is illustrated by the dotted lineand the dashed two dotted line. The position indicated by the dottedline shows the position in a configuration in which the length L3 of theopening 5 a is within the length L2 of the pressure generating chambers12, while the position indicated by the dashed two dotted line shows theposition in a configuration (configuration of FIG. 7) in which thelength L3 of the opening 5 a includes the length L2 of the pressuregenerating chamber 12.

As seen from FIG. 8, the displacement amounts Ah at the center of thepressure generating chamber 12 in the longitudinal direction issubstantially the same regardless of the above-mentioned difference ofthe length L3 of the opening 5 a. On the other hand, the displacementamounts Ah at the end portions of the pressure generating chambers 12are different such that the displacement amounts Ah are larger in theconfiguration in which the length L3 of the opening 5 a is longer thanthe length L2. When the displacement amounts Δh at the end portions ofthe pressure generating chambers 12 increases, the amount of liquidejected by flexing of the piezoelectric element 3. That is, according tothe modified example shown in FIG. 7, performance of the recording head1 can be improved by increasing the amount of liquid ejected. Moreover,in the configuration shown in FIG. 7, a vertical sectional view takenalong the line IVB-IVB is the same as that of FIG. 4B. Further, in avertical sectional view taken along the line IVA-IVA and a verticalsectional view taken along the line IVC-IVC, the opening 5 a is formedsimilarly to the vertical sectional view taken along the line IVB-IVB,and the upper electrode film 4 and the lead electrode 60 are disposed onthe opening 5 a.

5. Others

The above-mentioned recording head 1 constitutes part of a recordinghead unit having ink flow paths that communicate with the ink cartridgeand the like and is mounted on an ink jet recording apparatus which is aliquid ejection apparatus. FIG. 9 is a schematic view of an example ofthe ink jet recording apparatus. As shown in FIG. 9, cartridges 2A, 2Bthat constitute the ink supply unit are detachably mounted on therecording head units 1A, 1B having a recording head. A carriage 16 onwhich the recording head units 1A, 1B are mounted is provided on acarriage shaft 18 that is formed on an apparatus body 17 so as to bemovable along the carriage shaft 18. The recording head units 1A, 1B areconfigured to eject, for example, black ink composition and color inkcomposition, respectively. When a drive force from a drive motor 19 istransmitted to the carriage 16 via a plurality of gears (not shown inthe figure) and a timing belt 7, the carriage 16 on which the recordinghead units 1A, 1B are mounted moves along the carriage shaft 18.Further, a platen 8 is provided along the carriage shaft 18 in theapparatus body 17 such that a recording sheet S which is a recordingmedium such as a sheet of paper fed by a feeding roller and the like,which are not shown in the figure, is transported on the platen 8.

Although the ink jet recording head has been described as an example ofthe liquid ejection head of the invention, the liquid ejection head isnot limited thereto. The invention is generally directed to liquidejection heads, and as a matter of course, can be applied to heads thatejects liquid other than ink. Other liquid ejection heads may include,for example, various recording heads used for image recordingapparatuses such as printers, color material ejection heads used formanufacturing color filters for liquid crystal displays and the like,electrode material ejection heads used for manufacturing electrodes fororganic electroluminescence (EL) displays, field emission displays(FEDs) and the like, and bioorganic ejection heads used formanufacturing biochips.

Further, the piezoelectric element of the invention is not limited tothat used for the liquid ejection head, and can be used for otherdevices. Other devices may include, for example, ultrasonic devices suchas ultrasonic transmitters, ultrasonic motors, temperature-electricityconverters, pressure-electricity converters, ferroelectric transistors,piezoelectric transducers, block filters for harmful rays such asinfrared ray, optical filters using photonic crystal effect by quantumdot structure, and optical filters using thin film light interference.Further, the invention is also applicable to piezoelectric elements usedfor sensors, and piezoelectric elements used for ferroelectric memories.Sensors that use a piezoelectric element may include, for example,infrared sensors, ultrasonic sensors, thermo-sensitive sensors, pressuresensors, pyroelectric sensors and gyro sensors (angular rate sensors).

What is claimed is:
 1. A liquid ejection head comprising: a substrate inwhich a pressure generating chamber that communicates with a nozzleopening is formed; and a piezoelectric element having a piezoelectriclayer, a first electrode that is formed on a surface of thepiezoelectric layer on a side of the substrate so as to correspond tothe pressure generating chamber, and a second electrode that is formedon a surface of the piezoelectric layer opposite to the side on whichthe first electrode is formed so as to extend over a plurality of thepressure generating chambers, wherein the second electrode is formed toextend to an outside of the pressure generating chamber in alongitudinal direction of the pressure generating chamber.
 2. The liquidejection head according to claim 1 wherein an area where the firstelectrode, the piezoelectric layer and the second electrode overlap isformed to extend to an outside of the pressure generating chamber in thelongitudinal direction.
 3. The liquid ejection head according to claim 1wherein an opening is formed on the piezoelectric layer by removing thepiezoelectric layer at a position that substantially corresponds to anarea between the pressure generating chambers, and the opening is formedto extend to an outside of the pressure generating chamber in thelongitudinal direction.
 4. The liquid ejection head according to claim 1wherein a metal layer that is disposed on the second electrode andserves as a wiring is formed to extend to both inside and outside of thepressure generating chamber.
 5. A liquid ejection apparatus comprisingthe liquid ejection head according to claim
 1. 6. A liquid ejectionapparatus comprising the liquid ejection head according to claim
 2. 7. Aliquid ejection apparatus comprising the liquid ejection head accordingto claim
 3. 8. A liquid ejection apparatus comprising the liquidejection head according to claim 4.